Request Help Cleaning up Discarded Stage

[Lemit]

My first flight to the Mun left an expended Stage 3 in a deep elliptical orbit around Kerbin.   (that sounds familiar, Apollo 11)   Now I want to clean up local space a bit. (FYI, Jeb returned safely)

Can I attach a docking ring to the expended stage using EVA construction, dock with it, and push it back into a degrading orbit?  (assuming I can pull off the rendezvous)

For future efforts,  can I put a second command or Mechjeb on with reserve fuel,  and  fly it back to Kerbin?   I want to try to think and fly with some sense of environment conservation.  Any helpful ideas / discussions are appreciated. 

[tg626]

On my Mün landings I add a probe core to the transfer stage and make sure it has extra fuel.  After trans-münar injection, I seperate the craft from that stage, and switch to the jettisoned stage & alter it's course to crash into the Mün as was done with most Apollo missions - (11 relit the S-IVb to put it on a trajectory to get a gravity assist off the Moon and head off into solar orbit.)

I tend to try an make my designs self cleaning by staging my booster when Pe is still < 25km and so auto-destructs, adding retros to blindly slow a booster, or adding a probe core so I can send it to it's doom.

The Saturn V had it's own guidance system separate from the Command Module - so why not make my boosters "smart" too?

[Vanamonde]

If you have researched the Claw part you could also just fly up and grab the thing. 

[Zhetaan]

20 hours ago, Lemit said:

Can I attach a docking ring to the expended stage using EVA construction, dock with it, and push it back into a degrading orbit?  (assuming I can pull off the rendezvous)

Yes!  While the game tools do offer some easier options for this (such as the claw, as @Vanamonde mentioned, or even just deleting it from within the Tracking Station), this is a great way to practise rendezvous.  I will caution you to make certain that any docking clamp that you attach has its axis point through the centre of mass of the booster, if possible, or else you will get a surprise when you light the de-orbit engines.

20 hours ago, Lemit said:

For future efforts,  can I put a second command or Mechjeb on with reserve fuel,  and  fly it back to Kerbin?   I want to try to think and fly with some sense of environment conservation.  Any helpful ideas / discussions are appreciated. 

That can work, though you should be aware of which way the MechJeb module points.  Orientation is important for a probe core, and if what you think is prograde is a direction that it thinks is anti-normal, then you're going to have bad results.

If you want to pursue this seriously, then you might want to look at Stage Recovery to recover Funds.

Another option is to fly the booster into the Mun (the mod is a bit out of date, but I always thought that Impact! was a lot of fun, and Strategia, which is also somewhat out of date, has an impactor probe strategy).

If you want to try your hand at a flyback booster, then kOS is the mod for you.  There are quite a few scripts and script tutorials out there for building flyback boosters; the main problem is flying them while you have another vessel coasting to apoapsis.

Next, if you're interested in reusing the materials for some other project (and why not, since you went to the expense of getting the thing into space in the first place--David Brin's short story 'Tank Farm Dynamo' explores a similar concept, though with much harder science fiction), then you should look at Modular Kolonization System, or MKS for the ability to break down rocket parts into material kits that can be used to make other things in space.

Lastly, if you just want to blow things to smithereens without too much hassle, you have two mod options:  first is TAC Self-Destruct, which is exactly what it says on the tin, and the other is Kerbal Inventory System, or KIS, which has an explosive part that your engineer can attach to something that you would like to make go away.

Have fun!